Expression of tilapia prolactin receptor (tiPRL-R) has been characterised in the intestine, gill and kidney of tilapia species Oreochromis niloticus and the levels of both tiPRL-R transcripts and tiPRL ... [more ▼]

Expression of tilapia prolactin receptor (tiPRL-R) has been characterised in the intestine, gill and kidney of tilapia species Oreochromis niloticus and the levels of both tiPRL-R transcripts and tiPRL binding sites have been analysed in these organs during adaptation tilapia to a hyperosmotic environment. [less ▲]

The cDNA of the extracellular domain of rainbow trout (Oncorhynchus mykiss) prolactin receptor (trPRLR-ECD) was cloned in the prokaryotic expression vector pMON to enable its expression in Escherichia ... [more ▼]

The cDNA of the extracellular domain of rainbow trout (Oncorhynchus mykiss) prolactin receptor (trPRLR-ECD) was cloned in the prokaryotic expression vector pMON to enable its expression in Escherichia coli after induction with nalidixic acid. The bacterially expressed trPRLR-ECD protein, contained within the refractile body pellet, was solubilized in 4.5 M urea, refolded, and purified on a Q-Sepharose column, pH 8, by stepwise elution with NaCl. The bioactive monomeric 26-kDa fraction was eluted in 0.2 M NaCl, yielding 20 mg/2.5 L of induced culture. The purified protein was over 98% homogeneous, as shown by SDS-PAGE in the presence or absence of reducing agent and by chromatography on a Superdex column. Binding experiments using [125I]ovine placental lactogen (oPL) as a ligand revealed that human growth hormone (hGH), oPL, and ovine prolactin (oPRL) were the most effective competitors, with respective IC50 values of 1.32, 2.27, and 2.70 nM. Chicken (ch) PRL did not compete at all, and homologous trPRL was much less effective, with a corresponding IC50 value of 1826 nM. Gel-filtration was used to determine the stoichiometry of trPRLR-ECD's interaction with oPL, hGH, and oPRL. Only oPL yielded a 2:1 complex, whereas hGH and oPRL formed only 1:1 complexes, with excess trPRLR-ECD being seen at the initial 2:1 trPRLR-ECD:hGH or trPRLR-ECD:oPRL ratios. No studies were performed with chPRL because of its inability to compete with [125I]oPL or with trPRL because of its low affinity toward trPRLR-ECD. The present results agree with previous findings indicating, as in mammals, that homologous PRL interacts transiently with its receptor and suggest that transient homologous PRL-induced homodimerization of the receptor is sufficient to initiate a biological signal, despite the fact that, in classical binding experiments, only low specific binding can be detected. [less ▲]

A soluble protein that specifically bound 125I-human growth hormone (hGH) was identified in rainbow trout plasma, using HPLC-gel filtration. The binding affinity of the protein for hGH was 1.2 x 10(9)M-1. 125I-rainbow trout GH (tGH) was also able to bind to the protein albeit with a lower affinity (6.6 x 10(7)M-1) than hGH. Crosslinking experiments using 125I-hGH revealed two specific bands of 150 and 130 kDa. The complex 125I-hGH-BP could be precipitated by a monoclonal anti-GH receptor antibody, suggesting a close relationship between the plasma GH-BP and the GH receptor. A fourfold increase in the hGH binding to the GH-BP was shown 48 h after transfer of the fishes from freshwater to seawater. The increase in binding was related to a high binding capacity without significant changes in binding affinity. These results suggest a potential role of this related GH-BP as an index of GH effects during seawater adaptation in salmonids. [less ▲]

The aim of this study was to investigate the possible role of growth hormone in the adaptation of tilapia (Oreochromis niloticus) to brackish water and to analyze its interactions with prolactin in this ... [more ▼]

The aim of this study was to investigate the possible role of growth hormone in the adaptation of tilapia (Oreochromis niloticus) to brackish water and to analyze its interactions with prolactin in this process. Plasma levels of growth hormone do not change upon transfer to brackish water. Treatment of intact tilapia in fresh water with growth hormone prior to transfer did not enable the fish to preadapt to brackish water: the duration of the hydromineral imbalance after transfer was the same in treated animals and controls. The major osmoregulatory role of prolactin in fresh water led us to test the hypothesis that prolactin might antagonize the effect of growth hormone on adaptation to brackish water. Growth-hormone-treated hypophysectomized animals, however, exhibited no increased osmoregulatory capacity as compared to hypophysectomized controls, confirming the absence of a growth-hormone-related osmoregulatory effect. When prolactin and growth hormone were coinjected, growth hormone also proved unable to oppose the Na+ retaining effect of prolactin, in both brackish and fresh water. Surprisingly, hypophysectomized animals adapt better to brackish water than do sham-operated animals. This result is discussed in light of the effects of prolactin and cortisol on osmoregulation in brackish water and we suggest that an important event which allows O. niloticus to adapt to hyperosmotic environment is the reduction of plasma PRL upon transfer to brackish water. [less ▲]

A radioimmunoassay (RIA) for recombinant tilapia growth hormone (GH) was established and validated. The ability of various hypothalamic factors to regulate GH secretion in the tilapia hybrid (Oreochromis ... [more ▼]

Antisera to mammalian pituitary and placental hormones have been used to identify and localize the different cell types in the pituitary of the barbel (Barbus barbus, L.). The immunocytochemical labeling ... [more ▼]

Antisera to mammalian pituitary and placental hormones have been used to identify and localize the different cell types in the pituitary of the barbel (Barbus barbus, L.). The immunocytochemical labeling employed the immunoperoxidase technique or the immunogold silver staining procedure. Corticotrophic and prolactin cells, visualized using antisera to human adrenocorticotropic hormone and ovine prolactin (PRL), respectively, occur in the rostral pars distalis (RPD). Antisera against mammalian gonadotropins [ovine folliclestimulating hormone (FSH); bovine luteinizing hormone] or porcine growth hormone selectively cross-react with two different cell populations occupying the major part of the proximal pars distalis (PPD). Thyrotropic cells, stained by an antiserum to whole human thyroidstimulating hormone preabsorbed with porcine FSH, are scattered throughout the PPD and found amongst growth hormone and gonadotrophic cells. The majority of pars intermedia cells are stained with anti-melanophore stimulating hormone whereas the scattered PAS positive cells are revealed by both anti-ovine PRL and anti-bovine placental lactogen (or chorionic somatomammotropin). The latter antiserum also cross-reacts with the PRL cells of the RPD. Our results indicate that the distribution of the different cell types in Barbus barbus is similar to that described in other families of teleosts. This report is also the first demonstration of antigenic similarity between mammalian placental lactogen and fish prolactin. [less ▲]

In the present study, we have established and validated a radioenzyme assay which permits us to quantify progesterone metabolism in the chicken brain. Progesterone metabolism was then studied in five ... [more ▼]

In the present study, we have established and validated a radioenzyme assay which permits us to quantify progesterone metabolism in the chicken brain. Progesterone metabolism was then studied in five brain areas obtained by microdissection from the telencephalon (part of the lobus paraolfactorius immediately rostral to the preoptic area), the preoptic area, and the hypothalamus. Three metabolites of progesterone were produced in large amounts in these brain regions and were quantified in this study: 5 beta-pregnane-3,20-dione (5 beta-DHP) as well as its metabolite 3 alpha-hydroxy-5 beta-pregnane-20-one (5 beta,3 alpha-ol) and 5 alpha-pregnane-3,20-dione (5 alpha-DHP). The unmetabolized progesterone was also recovered and quantified. The 5 beta-reduction of progesterone (production of 5 beta-DHP and 5 beta,3 alpha-ol) was very active but its 5 alpha-reduction (production of 5 alpha-DHP) was almost absent in the lobus paraolfactorius. An opposite pattern of metabolism was found in the preoptic area and the hypothalamus (higher 5 alpha- but lower 5 beta-reductase activity). The changes in progesterone metabolism in these brain areas were then studied in groups of hens submitted to induced egg laying stop and molting. A significant decrease in progesterone 5 alpha-reduction was found in the median hypothalamus of hens during the period of molt. Simultaneously, the experimental procedures induced significant decreases in the production of 5 beta-DHP by the lobus paraolfactorius, anterior, and medial hypothalamus but induced a significant increase in the production of this metabolite in the preoptic area. These changes are likely to be involved in the control of reproductive functions including sexual behavior and secretion of luteinizing hormone-releasing hormone, and a number of possible causal mechanisms are presented. These should now be tested experimentally especially in view of the very limited information which is now available on the biological effects of the metabolites of progesterone. [less ▲]

The effects of testosterone, 5 alpha-dihydrotestosterone, and androstenedione on cloacal gland and sternotracheal muscle growth and on luteinizing hormone plasma levels were studied in Japanese quail. The ... [more ▼]

The effects of testosterone, 5 alpha-dihydrotestosterone, and androstenedione on cloacal gland and sternotracheal muscle growth and on luteinizing hormone plasma levels were studied in Japanese quail. The steroids were given to the animals in daily intramuscular injections and were dissolved either in propylene glycol or in ethanol:saline (1:1). The three steroids had significant effects on the responses which were measured, but the magnitude of this effect was clearly related to the type of vehicle in which the steroids were dissolved. Furthermore there was a significant interaction between the effects of solvents and of steroid; for example, testosterone was much less androgenic than 5 alpha-dihydrotestosterone when dissolved in propylene glycol, but both had similar effects when dissolved in ethanol:saline. The effects of the mode of administration of different steroids on a given physiological response should be taken into consideration. [less ▲]

Five experiments were carried out to study the role of the presence of a female on the reproductive endocrinology of male Japanese quail. In the first three experiments, exposure of an adult male raised ... [more ▼]

Five experiments were carried out to study the role of the presence of a female on the reproductive endocrinology of male Japanese quail. In the first three experiments, exposure of an adult male raised in long days to a female for l0 min or l week failed to increase plasma testosterone and LH levels; in fact a significant transitory decrease in plasma testosterone was observed, associated with a preceding increase in plasma corticosterone. These changes are interpreted as a result of the stress caused by repeated bleeding or by the continuous presence of a female in a limited space. In the last two experiments, an increase in the maturation rate of immature males could be observed in birds maintained in the continuous presence of females by comparison with birds kept in isolation. The paired males had larger cloacal glands and testes and higher plasma levels of testosterone and LH than the isolated one. This effect of the female was observed in long days (l6L:8D) as well as in marginally stimulating short days (l2L:l2D). [less ▲]

Seasonal variation in the levels of immunoreactive lutropin (LH), follitropin (FSH), prolactin (PRL), corticosterone (B), thyroxine (T4), and triiodothyronine (T3) was measured in the plasma of male and female capercaillies (Tetrao urogallus, Galliformes) in captivity (latitude N 67 degrees). In male capercaillies there was an increase in the concentrations of LH and FSH beginning in March and reaching their maxima in May, which correlated with the nesting period. The concentration of plasma PRL increased from the end of April and reached its highest level simultaneously with the rapid fall of plasma LH and FSH concentrations. It remained elevated until August, Plasma T4 level was depressed after levels of plasma FSH and LH had reached their maxima and was correlated to simultaneous elevation of plasma PRL level. No dramatic seasonal changes in plasma T3 level were noted. In the female capercaillie no marked changes in plasma FSH and LH concentrations were observed. Although four of six females laid eggs only one of them managed to terminate its nesting successfully; five eggs hatched. Changes in prolactin concentration in females parallel those in males. No marked variations were observed in plasma corticosterone concentrations. On the basis of these results it seems probable that captive female capercaillie show depressed gonadotrophin secretion, resulting in unsuccessful nesting. On the other hand it has to be emphasized that gonadotrophin assays may not be sensitive enough, especially in the female, to measure LH and FSH in the volumes of plasma put in the assays. [less ▲]

Three experiments were carried out to study whether differences in the intracellular metabolism of testosterone (T) can explain sexually differential responses to T in Japanese quail. In the first ... [more ▼]

Three experiments were carried out to study whether differences in the intracellular metabolism of testosterone (T) can explain sexually differential responses to T in Japanese quail. In the first experiment, a series of dose-response curves in which length of Silastic testosterone implants was related to effects on several behavioral and physiological variables was established. In Experiment 2, adult males and females were assigned to six experimental groups: intact males and females (I-males and I-females), castrated males and females implanted subcutaneously with 40-mm Silastic implants of T (T-males and T-females), and castrated males and females without hormone treatment (CX-males and CX-females). No CX-bird (male or female) and no I-female exhibited male sexual behavior. However, I-males and T-males regularly copulated during the behavioral tests. No crowing was ever heard in CX-animals and I-females. T-females crowed less than T-males and their crowing sounded weaker than those of males. The cloacal glands of T-females were less developed than those of males. Radioimmunoassay of T and 5 alpha-DHT showed that T-males and T-females have similar plasma levels of androgens. No striking differences were observed in the way testosterone is metabolized by the pituitary gland and central nervous tissues of males and females. By contrast, the production of 5 alpha-dihydrotestosterone (5 alpha-DHT) and 5 alpha-androstane-3 alpha, 17 beta-diol (5 alpha, 3 alpha-diol) was higher in the cloacal glands of males than in those of females. These sex differences were not detected between T-males and T-females. In experiment 3, the cloacal gland of males produced more 5 alpha-reduced metabolites than those of females. The pituitary gland of females also produced more 5 beta-androstane-3 alpha, 17 beta-diol (5 beta, 3 alpha-diol). In syringeal muscles, the production of 5 beta-dihydrotestosterone (5 beta-DHT) and 5 beta, 3 alpha-diol was higher in females compared to males. [less ▲]